1. Field of the Invention
The present invention relates to a speech codec which decodes an error-corrected signal (frame-structured received signal) in order to output decoded speech.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a prior art speech codec. In the figure, reference numeral 1 is a received signal; numeral 2 is an error-corrected signal output from an error correcting circuit after error correction, indicated later; numeral 3 is decoded speech obtained by decoding the error-corrected signal 2; numeral 41 is the above-mentioned error correcting circuit, and numeral 12 is a speech decoding circuit.
In operation, the error correcting circuit 41 decodes error-correcting codes in the received signal 1 so as to correct or detect any errors that may have occurred during transmission. The circuit 41 then outputs the error-corrected signal 2. The speech decoding circuit 12 decodes the error-corrected signal 2 to output the decoded speech 3.
Constructed as described above, prior art speech codecs have a drawback that, when the number of transmission errors in the received signal 1 exceeds the correcting capacity of error-correcting codes, wrong corrections and uncorrected errors which result cause the decoded speech 3 to contain noise.